During coronary bypass surgery, the main flow of the patient's blood is conventionally taken from the patient's vena cava, oxygenated in a heart-lung machine, and returned to the patient's aorta. Some blood, however, escapes into the surgical field, where it is conventionally aspirated by a sucker device and returned to the blood bypass circuit of the heart-lung machine through an appropriate filter which removes air bubbles and surgical debris.
A problem with cardiotomy filters is that when blood is aspirated from the surgical field, it is mixed with a great deal of air, which results in the formation of air bubbles. Due to the structure of blood proteins, these bubbles are highly stable. This is so because blood proteins are randomly oriented polar macro-molecules whose random orientation has a strong stabilizing effect. This process is different from the action of chemical stabilizers which are surface active, and it leads to the production of a foam which is difficult to break up by means of the chemical defoamers such as silicone compounds conventionally used in cardiotomy filters.
Quite aside from the difficulty of chemically defoaming cardiotomy blood, the use of defoaming agents in multi-layer filters, which are currently the norm, is physiologically undesirable and is traumatizing to the blood. Also, some foaming occurs as well in the venous reservoir which receives blood from the vena cava, and it would be advantageous not to have to make that blood pass through a defoaming filter. Consequently, there exists a need for a defoamer which is non-invasive, non-traumatizing, inexpensive and disposable, and which has a simple, essentially unobstructed blood path.